Applicants incorporate herein by reference any and all U. S. Patents, U. S. Patent Applications, and other documents and printed matter cited or referred to in this application.
It is common practice to analyze gases to determine the quantitative level of certain constituents (herein analytes) of the gas. Frequently, gases are analyzed for their oxygen content, particularly methane from coal or gas wells. The higher levels of oxygen in methane gas lead to corrosion of pipe lines and also may present a danger of explosion. When oxygen levels exceed, for example, 20 parts per million (ppm), an alarm or signal is given which is used to shut down the flow of methane from a well being monitored.
The instrument used to perform such analysis typically includes an assembly of discrete components including valves, valve fittings, flow meters, scrubbers, pressure regulators, needle valves, etc. Because of the numerous components, these instruments are very bulky, taking up space which could be utilized for better purposes. Most, if not all, of these discrete components are connected by tubing. The connections are prone to leak, particularly if they have to be broken and remade. Typically, the scrubber employed contains a material that removes deleterious constituents from the sample gas. This scrubber material changes color when exhausted and consequently needs to be replaced frequently, requiring disconnection of at least some of the components.
This invention has several features. Without limiting the scope of this invention as expressed by the claims that follow, its more prominent features will now be discussed briefly. After considering this discussion, and particularly after reading the section entitled, xe2x80x9cDETAILED DESCRIPTION,xe2x80x9d one will understand how the features of this invention provide its benefits, which include, but are not limited to, compactness, ease of assembly of components, ease of replacement of components when required, minimization of disconnection of components, and avoidance of leakage from or into the instrument.
The first feature of the gas analyzer instrument of this invention is that it includes a block having a sample gas inlet, a calibration gas inlet, and a gas outlet. Typically, the block has a height of from 3 to 4 inches, a width of from 3 to 4 inches, and a depth of from 1 to 3 inches. A valve and a detection cell are mounted to the block, with the cell being mounted in a manner that allows the gas being analyzed to flow past it. Typically, the detection cell is seated within a cavity in the block. The valve has a closed position, a sample gas position, and a calibration gas position. With the valve in the closed position or the calibration gas position, essentially all of the sample gas exits the gas outlet. With the valve in the sample position, a portion of the sample gas flows past the detection cell. The block includes (1) a first passageway extending from the calibration gas inlet through the valve and past the detection cell to the gas outlet, (2) a second passageway extending from the sample gas inlet through the valve and past the detection cell to the gas outlet, and (3) a third passageway that is in communication with the gas outlet.
The second feature is the use of a sample gas orifice and a bypass orifice. A calibration gas orifice may also be employed. The sizes of these orifices may vary, and in some instances within the same instrument, they have different sizes depending upon the application and environment under which the instrument is being used. The sample gas orifice is along the second passageway upstream of the valve, and the bypass orifice is along the third, passageway downstream of the sample gas orifice. As sample gas is being introduced through the sample gas inlet when the valve is in the sample gas position, at least a portion of the sample gas flows through the third passageway and exits the gas outlet. The size of the orifices is important for controlling the flow rate of gas through the instrument within a selected flow rate range over a variable gas inlet pressure over a given range. In a preferred embodiment of this invention, the gas introduced through either the sample gas inlet or the calibration gas inlet is within the range from 1 to 100 pounds per square inch gage (psig), and the orifices are sized so that the flow rate of gas through the instrument is within a predetermined range from 0.5 to 7 standard cubic feet per hour. Under these parameters, the orifices have an area from 0.00001 to 0.0005 square inch. When these orifices are substantially circular, they have a diameter from 0.004 to 0.022 inch.
In a preferred embodiment, the sample gas orifice is always in communication with the gas outlet through the bypass orifice regardless of the position of the valve. Consequently, at least a portion of the sample gas always exits the gas outlet as long as sample gas flows into the sample gas inlet. In one preferred embodiment of this invention, the instrument is designed so that most of the gas entering the instrument flows past the detection cell. This is not, however, critical. In some cases, particularly where it is desired to minimize the lag time between sampling a gas stream and testing of the sampled gas, most of the sample gas entering the instrument flows through the bypass orifice and out the gas outlet, and only a minor portion flows past the detection cell. In another case where it is desired to minimize the amount of sample gas being tested, most of the sample gas flows past the detection cell. In this case, the bypass orifice has a predetermined size that is substantially greater than the predetermined size of the sample gas orifice, preferably, the area of the bypass orifice is at least two times greater than the area of the sample gas orifice.
The third feature is that a scrubber is attached to the block upstream of the detection cell and down stream of the sample gas orifice. The scrubber removes from the sample gas unwanted substances, particularly those that have a deleterious effect on the cell. The scrubber comprises a see-through container made of either a transparent or translucent material. This see-through container holds scrubber material that removes the unwanted substances and changes color to indicate that the scrubber material is exhausted and needs replacement. The container is mounted to be detached from the block to provide access to the scrubber material to replace exhausted material. Preferably, there is a filter between the valve and the scrubber. The sample gas orifice and bypass orifice are also sized to maintain the pressure within the scrubber when the valve is in the closed position or the calibration gas position at a reduced pressure substantially below the elevated inlet pressure of the gas being analyzed, preventing a build up of excessive pressure in the scrubber when the valve is in either the closed position or the calibration gas position.
The fourth feature is that, in a preferred embodiment of this invention, gas leaves the block and then subsequently re-enters the block. In this embodiment, the second passageway has a first branch extending from the sample gas orifice through the block to a first outlet and a second branch extending from a first inlet through the valve and the detection cell to the gas outlet. The scrubber is connected between the first outlet and the first inlet to enable the sample gas to flow through the scrubber prior to flowing through the valve and past the detection cell. The sample gas orifice is along the first branch of the second passageway upstream of the first outlet. The bypass orifice is also upstream of the first outlet.
The fifth feature is that the instrument includes multiple flow paths. The calibration gas orifice is in communication with the gas outlet through a first flow path including the valve and the detection cell, and the sample gas orifice is in communication with the gas outlet through a second flow path including the scrubber, the valve, and the detection cell. The sample gas orifice is along the second flow path, and the bypass orifice is positioned between the sample gas orifice and the gas outlet, allowing a portion of the sample gas to exit the gas outlet. The first flow path and second flow path each includes a common flow path downstream of the detection cell. This common flow path has a first branch that extends through the block between the detection cell and an entrance port of a flow meter and a second branch between an exit port of the flow meter and the gas outlet. The second flow path includes a third branch that extends through the block from the sample gas inlet through the sample gas orifice to an entrance port of the scrubber and a fourth branch that extends through the block from an exit port of the scrubber to the valve.
The sixth feature is that the valve has a unique structure. It includes a cylindrical rotary member mounted within a cylindrical cavity in the block to rotate between the closed position, the sample gas position, and the calibration gas position. The rotary member has a side wall terminating at an inner face surface and a gas conduit extending between the rotary member""s inner face surface and the rotary member""s side wall. The inner face surface is perpendicular to the longitudinal axis of the cylindrical rotary member. The gas conduit terminates at one end in a first opening on the rotary member""s inner face surface and at another end in a second opening on the rotary member""s side wall. The cavity has a side wall terminating at a sunken face surface, and this sunken face surface has therein a first aperture in communication with the detection cell through the first passageway. There is a second aperture in the sunken face surface in communication with the scrubber through the second passageway, and a third aperture in communication with the calibration gas orifice through the third passageway. When in the sample gas position, the rotary member""s inner face surface covers the third aperture to prevent communication between the calibration gas orifice and the detection cell. When in the calibration gas position, the rotary member""s inner face surface covers the second aperture to prevent communication between the scrubber and the detection cell. When in the closed position, the rotary member""s inner face surface covers both the second aperture and the third aperture to prevent any gas from flowing past the detection cell. There are seal members surrounding the second and third apertures that bear against the inner face surface of the rotary member.
Other features include the use of a flow meter and a heater. The flow meter is mounted to an exterior surface of the block and is downstream of the detection cell. It has an exit port in communication with the gas outlet through a fourth passageway in the block that by passes the detection cell. The flow meter is in communication with the sample gas orifice, the calibration gas orifice, and the gas outlet in a manner that allows gas to flow through the flow meter prior to exiting the block through the gas outlet. The heater is mounted to the block, preferably within a cavity. A thermistor, connected in a control circuit for the instrument and mounted to the block next to the heater, compensates for the variation in cell output with temperature.
This invention also includes a method of measuring the amount of analyte in a sample gas. This method includes the steps of
(a) passing the sample gas by a detection cell mounted in a block having a plurality of passageways therein that direct the flow of gas between a gas inlet and a gas outlet,
(b) passing a calibration gas by the detection cell for calibration of said cell, said calibration gas flowing at least in part through a different passageway than the sample gas,
(c) controlling which passageway gas flows through by a valve mounted in the block and moveable between a first position when the calibration gas is to flow between the gas inlet and gas outlet and a second position when the sample gas is to flow between the gas inlet and gas outlet, and
(d) providing in the block a sample gas orifice along one passageway, and a bypass orifice in the block along another passageway positioned between the sample gas orifice and the gas outlet that allows a portion of the sample gas to exit the gas outlet when the valve is in the first position, said orifices being sized so that, with gas entering the instrument at an inlet orifice pressure within a predetermined range, the flow rate of gas through the instrument is within a predetermined range.